On 12.04.22 10:47, Vlastimil Babka wrote:
> On 3/29/22 18:04, David Hildenbrand wrote:
>> New anonymous pages are always mapped natively: only THP/khugepagd code
>
> khugepaged ^
>
>> maps a new compound anonymous page and passes "true". Otherwise, we're
>> just dealing with simple, non-compound pages.
>>
>> Let's give the interface clearer semantics and document these.
>>
>> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
>
> Nit:
>
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1182,19 +1182,22 @@ void page_add_anon_rmap(struct page *page,
>> }
>>
>> /**
>> - * page_add_new_anon_rmap - add pte mapping to a new anonymous page
>> + * page_add_new_anon_rmap - add mapping to a new anonymous page
>> * @page: the page to add the mapping to
>> * @vma: the vm area in which the mapping is added
>> * @address: the user virtual address mapped
>> - * @compound: charge the page as compound or small page
>> + *
>> + * If it's a compound page, it is accounted as a compound page. As the page
>> + * is new, it's assume to get mapped exclusively by a single process.
>> *
>> * Same as page_add_anon_rmap but must only be called on *new* pages.
>> * This means the inc-and-test can be bypassed.
>> * Page does not have to be locked.
>> */
>> void page_add_new_anon_rmap(struct page *page,
>> - struct vm_area_struct *vma, unsigned long address, bool compound)
>> + struct vm_area_struct *vma, unsigned long address)
>> {
>> + const bool compound = PageCompound(page);
>> int nr = compound ? thp_nr_pages(page) : 1;
>>
>> VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
>
> There's a VM_BUG_ON_PAGE(PageTransCompound(page), page); later in a
> !compound branch. Since compound is now determined by the same check, could
> be deleted.
>
Yes, eventually we could get rid of both VM_BUG_ON_PAGE() on both
branches and add a single VM_BUG_ON_PAGE(PageTail(page), page) check on
the compound branch. (we could also make sure that we're not given a
hugetlb page)
--
Thanks,
David / dhildenb
